text:
Is "MATON" real or did ChatGPT just make this up?
I was asking ChatGPT a few questions about NOTAMs, and decided to ask it what pilots use MATONs (NOTAM backwards) for. It "knew" from context that it had something to do with NOTAMs. It said this:

MATON (Military Aeronautical Telecommunications) is a system used by military pilots to access NOTAMs (Notice to Airmen) information. NOTAMs are issued by the Federal Aviation Administration (FAA) to provide important information about changes or potential hazards in the airspace, such as closed runways, temporary flight restrictions, and communication outages. Military pilots use MATONs to access NOTAMs information relevant to military operations, such as information about temporary flight restrictions (TFRs) or other airspace restrictions that are established for military exercises or training.
MATONs are used by the military to access NOTAMs information in a secure and encrypted format, in order to protect sensitive information about military operations. The NOTAMs information provided through MATONs is used by military pilots to plan their flights and navigate the airspace safely.
It's worth noting that while the FAA is responsible for issuing NOTAMs, the military also has its own NOTAM system, the MIL NOTAM, which is used to disseminate information relevant to military operations to military pilots and air traffic controllers.

Google couldn't find any military aeronautical telecommunications systems called MATON. Also, it would be an unusual acronym for Military Aeronautical TelecommunicatiONs; "MATEL" would make more sense. Did ChatGPT just make up an answer to my question? (It certainly isn't unheard of for ChatGPT to fabricate information, but this would be a particularly egregious case; it appears to have invented an entire military communications system based on only some context from a discussion of civil aviation and an acronym.)
I then asked it "Does MATON really exist?" and it said this:

I apologize, upon further research, it appears that MATON (Military Aeronautical Telecommunications) is not a system used by military pilots to access NOTAMs. My previous response was based on my knowledge cut-off and I apologize for any confusion this may have caused.
The FAA is responsible for issuing NOTAMs, which provide important information about changes or potential hazards in the airspace, such as closed runways, temporary flight restrictions, and communication outages. Pilots and air traffic controllers use NOTAMs to plan flights and navigate the airspace safely.
Military pilots also use NOTAMs to plan their flights, however, military operations may have specific and unique requirements that are not addressed by the civilian NOTAM system. To meet these requirements, the military may use a different system, such as the MIL NOTAM, which is used to disseminate information relevant to military operations to military pilots and air traffic controllers.
Again, I apologize for any confusion and any inaccuracies in my previous response.

Clearly one of its responses is wrong.

ChatGPT doesn't "make up" or "invent" anything. That is giving it far too much credit and demonstrates a very dangerous and unfortunately widespread misunderstanding about what ChatGPT is (and isn't). It strings together words that it has seen appear next to each other. That's all it does. Have you ever tried typing a message on your phone by only ever selecting the first suggested word on the predictive keyboard? Have you noticed that what comes out typically makes no sense but still sounds at least remotely like a message you might have written? That's how ChatGPT works, except with a …

… way bigger training set. But the principle is the same: GPT-3 gets fed pretty much everything ever written in the history of mankind, breaks it up into pairs of tokens, for each start token, it analyzes what's the most likely following token, and stores that. Then, when you ask it to produce a text, it will just start with a token, predict the most likely next one, then the next, then the next, and so on.

@JörgWMittag what word would you suggest using when ChatGPT generates text about something that doesn't [appear to] exist?

I'd call that "working as intended". It is designed to pass the Turing test, i.e. to fool people, not to be correct, precise, or accurate. In fact, that would defeat the point, since people aren't correct, precise, or accurate, so you would be able to tell it's an AI by its correctness, precision, and accuracy.

As my oldest kid the software developer says, AI is a hype term for just really really fancy software.  Still garbage in/garbage out.  BTW they just changed the "Airmen" part of NOTAM to "Air Mission" to achieve certain social language objectives, which now appears to be the FAA's priority.

@JohnK having developed a program that is on the simple end of what many people would consider "AI" (far simpler than ChatGPT), I definitely agree that it's not the big deal people think it is. "Machine learning" is a more meaningful term IMO.

Chatbots are designed to imitate a human interaction, until their accuracy dramatically improves I would consider every question based on chatbots to be off-topic.

The OP has the necessary info to answer the question:

Google couldn't find any military aeronautical telecommunications systems called MATON.

No, MATON isn't a thing.
As Stack Exchange notes in the Why posting GPT and ChatGPT generated answers is not currently acceptable page,

Stack Overflow is a community built upon trust. The community trusts that users are submitting answers that reflect what they actually know to be accurate and that they and their peers have the knowledge and skill set to verify and validate those answers. ... Currently, contributions generated by GPT most often do not meet these standards and therefore are not contributing to a trustworthy environment.

GPT isn't a person, and it is written to provide a "looks good" answer, not necessarily an "is correct" answer. To say that is has zero integrity and is willing to lie convincingly isn't wrong, but that's as much because integrity & a concept of doing the right thing is only applicable to humans, while GPT is a program. It's doing what it's programmed to do.
This experiment demonstrates vividly why GPT is not to be trusted, and why SE is right to ban it.
Note that the policy of suspending users who post GPT content without attribution (i.e. the OP is fine here) is a zero tolerance & no warnings policy; a few accounts have already received significant suspensions for posting GPT-generated content on Aviation.SE.

Note that the original ban is only about questions and answers generated by GPT. However, there is also currently a discussion about the scenario we have here: asking about something generated by GPT. For this case, the consensus also seems to be to ban it completely, because a) the answer is always the same: Is it true? "No!" Why did GPT say this? "Because it just randomly strings together convincingly-sounding gibberish". and b) the fact that you can, with zero effort, generate an infinite flood of such questions, each of which require non-zero effort to answer, is essentially a DoS attack

Such questions also almost always qualify for downvotes as "does not show any research effort" since ChatGPT's limitations are clearly listed on its introductory blog post under the heading "Limitations", one of which is "plausible-sounding but incorrect or nonsensical answers".


text:
What's the smallest 3-blade propeller for this motor?
I've got a 15470 brushless 35kw motor from China
How do I find the smallest 3-blade propeller I can use for this motor?
Here are it's specs,
Max Power: 35KW
Max Amp: 400A
Max RPM: 8500
Max Volt: 120v
Torque: 75Nm
Resistance: .94
I've looked into eCalc but it's for determining power / thrust, etc and not finding prop size.
Any help would be appreciated!

"Because 120 * 35 our maximum RPM would be 4,200" - Come again? You can't get the maximum RPM by multiplying the voltage by the power.

Since you're looking for "smallest prop", how much thrust do you need out of it and how much torque can your motor supply at 4200 rpm?

@DanPichelman I've added more detail to the question, the manufacturer recommends a 36-40 inch 2-blade propeller, so I was wondering how to calculate an equivalent 3-blade propeller (or do I just take off an inch as is the "rule of thumb"?)

Seems like the pitch of the propeller would matter quite a bit here as well.

I seriously doubt that thing is rated for life safety.  You would need to use it in a jurisdiction that has lax safety regs.

You need the largest prop that keeps the tip speed below about .9 Mach, roughly 1000 ft/sec, so you want the largest propeller than can operate at that RPM at .9 mach.  Here's a tip speed calculator for larger propellers that should suffice.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Why do Audio Engine Fail Alarms not state which engine has failed?
When an engine fails on e.g. a 737, an alarm sounds to indicate an engine fire (but not failure). Why however, is there no verbal alarm stating which engine has failed, in the same way that "TERRAIN, TERRAIN" warnings exist - why does it not state "RIGHT ENGINE FAIL"/"NO.2 ENGINE FAIL"?
I ask this after there have been numerous incidents in which the incorrect engine has been shut down, leading to effectively dual engine failure, such as:
British Midland 092
https://en.wikipedia.org/wiki/Kegworth_air_disaster
SA Airlink 8911
https://en.wikipedia.org/wiki/SA_Airlink_Flight_8911
I understand there were many factors that led to these crashes, such as poor CRM, but my question still stands.
Cheers

Related definition of warning vs. caution alerts, and aural signals for the US. This link is extracted from this unanswered question: Aural alerts for advisory function. This itself explains why a single engine failure is not at the same level (aural) than "Terrain! terrain!", but it doesn't answer other elements in your question.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Why don't airliner vertical tails extend to the very aft of the fuselage?
Looking at several modern airliners, the root of the vertical tail doesn't extend right to the aft-most point of the fuselage. This seems counter-intuitive given extending the tail further aft would increase the moment arm and its contribution to the aircraft's directional stability.
In this photo of a 787, you can see what I mean.

There is still a significant length of fuselage behind the tail.
The same can be said for the A320:

This is far less prevalent on the 737 Classics and NG

And the BAE-146 follows (to my ignorance) what seems like the most logical tail design, with the root reaching the very aft of the fuselage.

The potential reasons for the tail not extending fully aft, that spring to mind are:

CG limits
APU placement
Torsional loads on the fuselage where it becomes very thin at the back, not being able to support the loads imposed by the tail.

Is this why it is or is there more to it?

"CG limits
APU placement
Torsional loads on the fuselage" So, you have basically answered your own question

@sophit ah yes I presumed there was more to it than that but maybe that's it...!

@sophit ok thank you - so to that end, it seems to me to make the most sense to put the tail further aft and have a longer APU exhaust with APU a bit further fwd to allow tail structures to be put in. Then there's a less aft CG and longer tail moment arm, meaning the tail can be smaller (less weight and wetted area)?

@sophit Nobody in their right mind oversizes a tail surface. The A318 vertical is larger than that of an A320 precisely to compensate for the shorter lever arm.

@PeterKämpf: correct, I meant A319 Vs. A321, which all share the same tailplane.

Are there any aerospace examples of applying a boat tail?

If 'several modern airliners' matters here, how do you see 'several' as different from 'all', please?

The three main duties of a vertical (as well as horizontal) stabiliser are:

to trim;
to control;
and to provide with stability the airplane.

the root of the vertical tail doesn't extend right to the aft-most point of the fuselage

All of these three characteristics develop in respect to the CG and/or the aerodynamic center AC of the airplane and it is therefore the distance from CG/AC which enters in the design process of the tailplane and not the distance from the fuselage's end. Where the fuselage actually ends has nothing to do with  the sizing/location of the tailplane: the tailcone simply aerodynamically "closes" the fuselage, possibly taking into account the area rule like it was done for example for the Concorde; obviously this is not important for general aviation airplanes. Tailcone can be used for example also to hold the APU: this location for the APU is ideal since it is far from any important structure or pipe that could be damaged in case of APU's failure; it is easily accessible; the exhaust is short and straight and doesn't point toward anybody.

This seems counter-intuitive given extending the tail further aft would increase the moment arm

The sizing condition for the vertical stabiliser is normally given by stability against Dutch-roll and, for the rudder, by landing @OEI. Locating it further aft would maybe reduce its size and weight but at the expense of a longer and heavier fuselage's structure. The tailplane can even be designed keeping in mind future stretching/shrinking of the fuselage's length like in the case of the A319, A320 and A321 which all share the same tailplane.

is there more to it?

At least two other points come to mind:

as already pointed out in another answer, for spin recovery is indeed important the longitudinal placement of the vertical stabiliser but, again, not in respect to the fuselage's end rather in respect to the horizontal stabiliser: this latter should be placed well forward or well backward in respect to the vertical stabiliser, as can be seen in the following picture (source) together with the rule of thumb for a safe spin recovery (rudder as much a possible outside the tailplane's wake extending 60° and 30° upward):

Anyway this is less of a concern on modern jetliners where the avionics (try to) keep the aircraft far from this condition. Off the top of my head I don't think that any modern jetliner with conventional tailplane respects this rule of thumb.

structural clearance between horizontal and vertical stabiliser: by a structural point of view, the horizontal stabiliser is only one single piece going through the fuselage, just like the wing. That means that no important structure can be placed at the same fuselage's station: the structure of the vertical stabiliser is attached to the fuselage just in front of (or behind) the horizontal stabiliser. This can be seen for example in this B737's cutaway:

The horizontal stabiliser's structure 118 goes through the fuselage and the vertical stabiliser is attached just in front of it 99.

Spin resistance and area ruling
Locating the vertical a bit ahead of the horizontal tail brings it out of the probable wake of the horizontal at high angle of attack, so it still is effective in damping the yawing motion. If this were not the case, the airplane would be much harder to bring out of a spin.
As you correctly note, the T-tail of a BAe 146 allows to put the vertical all the way back. Same for the DC-9 and most other T-tails.
The Boeing 727 and the Tu-154 have a longer fuselage because they have the hot parts of the center engine at the end of their fuselage. Other T-tails (Fokker 28 / 100, Tu-134) can afford to move the vertical all the way back.
The APU is small enough so it will not force a less than ideal tail placement.
EDIT:
Phil Sweet's answer adds another good point: Area ruling. Placing horizontal and vertical tail a bit apart helps with area ruling. Which one comes first, however, is determined by high angle of attack aerodynamics.

If the APU is within the aft fuselage ahead of the last bulkhead, it will be in a stainless steel enclosure box for fire protection and containment. Most however put it after the last bulkhead that has the fin main spar so it is outside the structural hull and enclosed only by an aerodynamic tailcone fairing that is more or less a cowling.

For fast aircraft, there is a drag penalty. You want the curve of cross-sectional areas to be nice and smooth. If the tail is right at the back, then there is a big lump at the rear of the area curve.

Whitcomb area rule: https://en.wikipedia.org/wiki/Area_rule
The area rule says that two airplanes with the same longitudinal cross-sectional area distribution have the same wave drag, independent of how the area is distributed laterally (i.e. in the fuselage or in the wing). Furthermore, to avoid the formation of strong shock waves the external shape of the aircraft has to be carefully arranged so that the cross-sectional area changes as smoothly as possible going from nose to tail. At the location of the wing, the fuselage is narrowed or "waisted". Fuselage cross-sectional area may need to be reduced by flattening the sides of the fuselage below a bubble canopy and at the tail surfaces to compensate for their presence, both of which were done on the Hawker Siddeley Buccaneer.1

You can't flatten something that isn't there. You have to shift the tail forward to be able to flatten the fuselage and make significant volume adjustments.
Taking this one step further, sometimes you have a tail-like junction of foils without a fuselage, such as a T-foil hydrofoil. In that case, you can actually lower total drag by adding an extended fairing body to lower the junction drag. Coke bottle fairing (Tspeer is an aero guy with a boating side-hustle.)

If there's a need to obey the area rule then it's better not to move the whole stabiliser forward, possibly altering its stabilising effect and needing a bigger and heavier one, but it's enough to simply prolong the tailcone backward just like they did for example with the Concorde as explained in the Wikipedia link.

Sweep takes care of the area rule. No need to extend the fuselage. But placing horizontal and vertical tails a bit apart is indeed helpful in getting the area distribution right.

@PeterKämpf: well, Concorde's engineers did extend the fuselage without touching the stabiliser

@PeterKämpf, perhaps counterintuitively, sweep doesn't really help much. I actually apply sweep when I'm producing the area rule curve, so it cancels out. But I don't design planes, I am an amateur boat designer. We have essentially the same area rule in the form of a displacement curve. But near the surface, it works better if you apply sweep when producing the curve. We "bustle" the stern in front of the rudder to improve wake drag. The near-surface regime in a boat is mathematically identical to the transonic regime in planes.

@PeterKämpf  Also, the taper really diminishes the outboard volumes, so the area curve is dominated by the root sections. The spanwise rake of the foil areas is usually less than the aerodynamic sweep angle due to mechanical design constraints.

DRAG REDUCTION OBTAINED BY THE ADDITION OF A BOATTAIL TO A BOX SHAPED VEHICLE https://www.nasa.gov/centers/dryden/pdf/87934main_163113.pdf ... "Projectiles designed for supersonic use often have a slightly tapered base at the rear, called a boat tail, which reduces air resistance in flight." https://en.wikipedia.org/wiki/External_ballistics#General_trends_in_drag_or_ballistic_coefficient - The Concord needed an actual 'rain drop'; a boat tail wasn't going to cut it.

'The duties of a vertical (as well as horizontal) stabiliser are' neither here nor there. Why is there a tip sticking out of the back end? Drag, +1.


text:
Can the 737 Max autopilot be engaged when some sensors have failed?
If some instruments on the 737 MAX 8 fail on the Captain's side and autopilot stops, can the First Officer engage autopilot (as the instruments on his side are fine)?  In the ET 302 crash the Captain tried to engage the auto pilot but it kept disengaging because of bad AoA readings (which in turn also affected other readings).  Could the First Officer have engaged the autopilot as instruments on his side were working fine?

The following applies to the Boeing 737 NG series, but probably there are no large differences for the MAX series.
The FCOMv2 (4.20.2 Automatic Flight - System Description) mentions only the following systems in the Autopilot Engagement Criteria and the Autopilot Disengagement sections:

The A/P automatically disengages when any of the following occurs:

[...]
either left or right IRS system failure or FAULT light illuminated
loss of electrical power or a sensor input which prevents proper operation
  of the engaged A/P and mode
loss of respective hydraulic system pressure.

Note: Loss of the system A engine-driven hydraulic pump, and a heavy demand
  on system A, may cause A/P A to disengage.

The sensor input is probably what you are asking about because this would affect the instruments as well. In general, if a system only affects one side, the other autopilot should still work. One notable exception would be the IRS, where any IRS failure causes the autopilot to disconnect.

Edit:
The two autopilot systems on the 737 are called A and B, and they are not necessarily linked to Captain and First Officer. Both the Captain and the First Officer can press both engagement buttons on the MCP (marked with 1 in the image from the FCOM below).

But does channel A use left side data and channel B right side data, or both channel all three data?

It depends.  There are some failures that inhibit both autopilots, and others that may affect only one.  Also, policy may be more restrictive -- the QRH may direct not engaging the affected-side autopilot, or it may direct to not engage either autopilot, even though the system wouldn't inhibit it per se.
Please note that "instruments" on the Max (and NG) are almost all displayed on the screens.  If a screen fails, it probably won't affect either autopilot, although if the failure is far enough back in the black boxes (say, a DU or something at that level of hardware), it might.  The failures that can inhibit autopilot engagement are more typically within systems, not instruments.

Thanks Ralph. Have added to my question to make it clearer.

@OutOfTheBox  Your edit made the question into speculation about an accident, which is off-topic. It would be better to revert it to what you had before. I'm not going to speculate about hypotheticals in that crash.

My question was based on the data recovered from the Flight Data Recorder and Voice Recorder.  The left side had stick shaker and different AoA, Airspeed and Altitude than the right side.  I suspect the AP failed to engage because of the stick shaker and / or unacceptable values.  If so, could the other AP have been engaged, as I assume the other AP uses values from the right side which were still good.  That is the question.


text:
How to make an airplane less bumpy?
Other than the weight (which to my understanding is the number one factor i.e. a heavier airplane will fly more smoothly than a light airplane), which factors of the airplane design make an airplane more or less bumpy?

Similar

When you say weight -- a heavier aircraft is less bumpy, what you're really after is the wing loading.  A heavier aircraft with a smaller wing will be less bumpy.  The bigger the wing, the more susceptible to gusts.
A flexible structure (particularly in the wings) will help as well.  When gusts hit the wings, they will deflect and not transfer those disturbances into the fuselage as much.  Flexible wings act like the suspension on a car.
Some aircraft now use active measures to suppress gusts.  When a gust is detected, an active computer controlled system will deflect control surfaces to dump or increase lift on part of the wing in response to the gust.  These systems not only reduce the bumpiness of the ride for passengers, they can actually reduce the structural limits that the aircraft must be designed to and thereby can allow the engineers to design a lighter wing.
Here are some videos of the gust alleviation system on the 787.
On YouTube
On Facebook

Hey do you have a link or video that explains the computerized control system for gust suppression? I really would like to see it

Here are some ways to reduce bumpiness.

design the plane to fly higher, where the air is less bumpy.

design the plane to fly faster, so it spends less time in a rising or descending air column so its inertia will have a better chance of "clamping" it against perturbations.

design the plane with "springier" wings (i.e., with a more flexible main spar) to help smooth over the bumps.

Regarding this last effect, it is claimed that the M20-series of Mooneys which had a wooden main spar furnished a smoother ride than the later models that had metal spars.


text:
Is it normal for a Boeing 757 engine to bounce under its fairing?
Earlier this week I was on a 757 flight from SFO to JFK and the right engine was bouncing under the fairing under mild turbulence, and really moving 2+ cm under moderate turbulence. Is that in any way normal or cause for concern? Here's a video of the bounce with very mild turbulence. To see the bounce, zoom into the seam where the nacelle meets the fairing: https://drive.google.com/file/d/1QpegQ0FOUhJrp8vqMrshtCdBQDyJTWO0/view

Looks perfectly normal to me. When flying as a passenger, I've observed pylon mounted engines bounce a lot more than that. And when flying as a 747 captain in significant turbulence, I used to look out the side window back at engines 1 & 2 and watch them really bounce around.

Yes, it's normal. You will see engines bounce, yaw and shake, sometimes with apparently alarming ferocity, and you might wonder whether something is going to shake itself apart.
However, the fact is that the engines bounce because they can. Their mountings - which are extremely strong - are absorbing a lot of movement and energy safely. For example, they have to be able to handle the immense thrust that the engine puts out for the whole flight.
Another thing that you need to bear in mind is that many visible parts are themselves more flexibly attached to hidden and more stiffly mounted ones that are attached to each other. So you're not just seeing movement of structural parts, but that, plus the movement of the lighter, flexible coverings.
In short, there is nothing there to worry about, though it can be unsettling to see.


text:
When are pressure-swirl atomizers and airblast atomizers used?
I am a little confused as to when (during T/O, cruise, etc.) and how the combined pressure-swirl atomizer and airblast atomizer is used.
Lefebvre writes that "the merits of the pressure-swirl atomizer at low fuel flows, namely, easy lightup and wide stability limits, are combined with all the virtues of airblast atomization (notably a soot-free exhaust) at high-fuel flow rates."
From this I understood, that if a combined pressure-swirl and airblast atomizer is used, then the swirl atomizer would be more used during cruise (lower fuel flow rates) and the airblast more during takeoff (higher fuel flow rates).
However, it is also stated by the author just before that for an airblast atomizer "The major practical disadvantages are rather narrow stalobility limits and poor atomization quality at startup, owing to the low air velocity through the atomizer."
At takeoff isn't the air velocity lower? And if that is the case, then this for me puts into question the use of the airblast during takeoff.
So are the conditions for the airblast atomizer: high fuel flow rate and high velocity and for swirl atomizer: low fuel flow rate and low velocity?
If so, how do they interact during engine operations?
All citations are taken from Chapter 1 of Gas Turbine Combustion by Lefebvre.
I know I am wrong and I would love to know why. Thank you for your help!


text:
Why did this aircraft take off in the opposite direction compared to the one used by other flights right before/after it?
I recently took a weekend trip to Naples and went to admire the city from above at the Certosa di San Martino panoramic viewpoint which, it turned out, was also offering a distant view at NAP operations that morning (June 15, 2019, around 12PM CEST). After taking a few pictures I couldn't help but spending a good 15 minutes tracking a few landings and departures with the FlightRadar app.
Runway 24 was in use at that time, except for a single departure in that timeframe which used runway 6.
Is this a common scenario - i.e. a single aircraft taking off from the runway opposite to the one currently in use?
I know the general factors taken into account when determining in which direction a runway is used, but what could be the reasons behind such a sudden and isolate (takeoffs and landings just 3 minutes before/after used runway 24) change in the airport operations?
The aircraft in question left NAP with more than 1 hour delay, leading me to think that it could have been pilot's request to spare a few minutes: probably positioning for 6 was faster from their gate?

It looks like the reason for the Rwy 6 departure was noise abatement. The climb gradient from 6 is not as steep as for 24. The Jeppesen charts state the requirements:

And it states that if you are unable to comply with the steeper noise abatement climb gradient for rwy 24 (583 ft climb per nautical mile), you should request 6 (300 ft climb per nautical mile). Maybe the plane was fully loaded and the captain wanted to avoid a fine.

can confirm. this is the METAR at the time:
SA  15/06/2019 12:20-> METAR LIRN 151220Z 20006KT 170V240 CAVOK 31/18 Q1015 NOSIG= SA  15/06/2019 11:50-> METAR LIRN 151150Z 20007KT 170V240 CAVOK 30/19 Q1015 NOSIG=

Light winds some 40 degrees from rwy heading. I don't think that would be reason to deny the takeoff request.

Aha! A clue, Sherlock! Good one.

@JuanJimenez Isn’t LIRN one of the places where financial noise penalties are easily contracted?

@CptReynolds Not a clue, but that might explain the t/o rwy requests. The aircraft was an A319, but I don't know under what conditions it might not be able to meet noise abatement restrictions. Loading? OAT? Beats me. Someone above my paygrade ought to be able to comment on that.

@CptReynolds Whoa. We got ourselves a winner, exactly what @ ymb1 stated. Changed the answer to point specifically at noise abatement climb gradient requirements.

Strange that I cannot find what the fines are for noise abatement violations...

I was stationed at the naval base at Capodichino, with my room overlooking the runway (I'm not a pilot). C-5 Galaxies would always take off to the west it seemed. I guess they could make the gradient? They were very loud when taking off. And their exhaust would blow right into my room after they taxied in or were starting up.

@Steve But don't you love the smell of jet fuel in the morning? :)


text:
Are any Q-codes still used in aviation?
On amateur (ham) radio, we often use Q-codes, which are three-letter codes starting with the letter Q with various meanings. They were originally used to speed up Morse code communications; it might be necessary to send "Can you hear me between your signals and if so can I break in on your transmission?" fairly frequently, but you would not want to send that entire sentence regularly. "QSK?" is much shorter. Many of the codes still in common use aren't used exactly "correctly"; they've become more jargon than codes. "QRP," for example, actually means "Shall I decrease transmitter power?" and "Decrease transmitter power," but it's more commonly used as an adjective meaning low-power; you might have a QRP transmitter, meaning that the transmitter has a low maximum power setting. "QSO" means "Can you communicate with...?" or "I can communicate with...," but now often means a radio contact (as a noun); a "QRP QSO" is a contact in which one or both operators was transmitting at low power. (I don't use CW and I rarely use conversational digital modes; these codes might be used "correctly" more often on those modes.) Pronunciations are not always "correct" either; I hear people say "queue so" instead of "queue ess oh" fairly often.
There are (were?) a lot of these codes specifically intended for aviation. Are any of them still used, either the "right" way or as jargon?

The three main ones still in use relate to altimeter settings.

QFE refers to the current atmospheric pressure at a specified point (generally the field elevation reference point, or a runway threshold). As such, if a pilot sets their altimeter to QFE, their altimeter will read their height above that point.
QNH refers to the current atmospheric pressure at mean sea level. If a pilot sets their altimeter to QNH, their altimeter will read their AMSL altitude.
QNE refers to the value an altimeter will show when it is at the specified runway threshold, if the altimeter is set to the "standard" 29.92 inHg or 1013.25 hPa. As slang, it refers to that standard altimeter setting. This is not perfectly correct usage.

The Wikipedia entry for Aeronautical Code signals additionally lists QFF, QDM, QDL, QDR, QFU, QGE, QGH, QTE, QTF, and QUJ as being in use today. I am not sure how accurate that is; the article was created in March 2015 and is substantially unchanged since then.

In my 30+ years in US ATC, I never saw/heard any of them used ever. It must be an overseas thing.

Another I hear fairly regularly in UK aviation is QSY which falls somewhere between actual usage and "slang". It's a quick way of signalling to a controller that you want to change frequency (especially if they are busy) or for them to tell you to change frequency whenever you like.
I commonly hear this when crossing Luton, which is a fairly busy regional London airport.
Either from them

G-ABCD, leaving controlled airspace in 1 mile QSY (my destination airfield close by) en-route

or from me

G-ABCD, at (exit point of controlled airspace) happy to QSY (my destination close by)

When the controller is less busy, we tend to use more standard communication.


text:
Who was the first person to fly above 20,000 feet, and what aircraft was used?

Oh! I have slipped the surly bonds of Earth
And danced the skies on laughter-silvered wings;
Sunward I’ve climbed, and joined the tumbling mirth
of sun-split clouds, — and done a hundred things
You have not dreamed of – wheeled and soared and swung
High in the sunlit silence. Hov’ring there,
I’ve chased the shouting wind along, and flung
My eager craft through footless halls of air....
Up, up the long, delirious, burning blue
I’ve topped the wind-swept heights with easy grace.
Where never lark, or even eagle flew —
And, while with silent, lifting mind I've trod
The high untrespassed sanctity of space,
– Put out my hand, and touched the face of God.

("High Flight" by John Gillespie Magee Jr.)
From what I've seen, it seems that eagles can fly up to about 20,000 feet. Who was the first human aviator to reach this altitude in sustained flight, and what aircraft was used?
If the initial record was not set on an aircraft with wings, I would also be interested in the first time it was done in a fixed-wing aircraft, because while a balloon pilot may have "slipped the surly bonds of Earth," they have not "danced the skies on laughter-silvered wings."

20,000 ft was a common patrol altitude for pilots on Dawn Patrol in WW1. That altitude is tolerable without oxygen for short periods if you're acclimatized to it.

Étienne Gaspard Robert (sometimes Robertson), a Belgian stage magician, certainly claimed to have reached 7,171 metres (23,526 feet) in July 1803, which is the record stated by Wikipedia. This was in the balloon L'Entrepement which had first flown in 1794, and had been used in the Napoleonic wars.
There is some doubt as to his claim, in particular scepticism that such a small balloon could reach that altitude carrying two people, and his "outlandish description of the effects of the high altitude".

L'Entreprenant used by the French Republican Army to observe the combined Austrian and Dutch army at Maubeuge on 26 June 1794. This became the first battle to be won through control of the air.
A more authoritative experiment took place a year later:

The scientists J.B. Biot and Joseph Louis Gay-Lussac made
electromagnetic observations in their flight from the Conservatoire
des Arts et Métiers in Paris on August 24, 1804. According to their
barometer, they rose to 13,000 feet (3,962 meters).
Later, Gay-Lussac
made another flight by himself and ascended to 23,000 feet (7,010
meters) — a record that was held for 50 years. At that height, he
experienced quickened pulse, shortness of breath, and finally
unconsciousness—symptoms of oxygen deprivation — until the balloon began
to descend. He still managed, however, to collect air samples at over
20,000 feet (6,000 meters), study the variation of pressure and
temperature, and repeat his earlier electromagnetic observations.

source
So we can't really be sure who was the first aviator, though I'm more inclined to accept 1804. It's also worth mentioning that the Incas had ascended mountains higher than 20,000 feet by the fifteenth century.

If you're counting mountain climbers, there's probably some earlier climbers in the Himalayas as well.  Maybe not Everest itself, but there's plenty of land above 20,000 ft in that region.

@DarrelHoffman: Did any of them throw a paper airplane while above 20k feet?  Or jump in the air perhaps?  :P

Fly.  The key word in the question is fly...

@PeterCordes - I'm assuming Darrel's comment was referring to the bit in this answer referring to the Inca, not to the question itself.

Pretty sure Sherpas and other natives have been travelling over Himalayan passes higher than 20,000 ft since the year dot -- carrying heavy loads on their backs! Acclimatization works wonders.

@nigel222 so one of them could safely, albeit not legally, fly an unpressurized plane at 20,000 feet without supplemental oxygen?

@Someone Yes (assuming they were  a qualified pilot).

According to Wikipedia in a balloon:

1803-07-18: 7.28 km (23,900 ft); Étienne-Gaspard Robert and Auguste Lhoëst in a balloon.

and fixed wing:

1916  November 9  26,083 ft   7,950 m     Guido Guidi     Caudron G.4     propeller   Torino Mirafiori airfield


text:
What was the needle on the nose of Space Shuttle Enterprise for?

What is the purpose of the needle-like object on the nose?
Why do experimental aircraft such as the X-35 have such long Pitot tubes? is related but not a duplicate; it does not actually say what the object is, because it doesn't mention the space shuttle. Just because some experimental aircraft have long pitot tubes on the nose doesn't mean that any needle-like object on the nose of an experimental aircraft is necessarily a pitot tube. Even if an object like this on an aircraft is always a pitot tube, that's not obvious to a non-expert, even after reading that question and its answers.

Actually, I think that indeed any needle-like object on the nose of an experimental aircraft is a pitot tube :)

@U_flow that might be the case, and it might even be obvious to experts, but it isn't obvious to a non-expert, even after reading the linked question.

@Someone sorry, my comment was not meant to be an insult. But the more I think about it, the more I think it is actually true. These are always pitot tubes, or pitot tubes combined with Angle of attack and sideslip sensors.

I didn't think your comment was an insult; sorry if mine came across that way.

The "as duplicate of" question doesn't mention the space shuttle, but the answer to it discusses how "When test flying new aircraft long pitot tubes ... are used to ensure the probes are free of any interference the body of the aircraft may cause." So the question isn't identical, but the answer there applies here.  That understanding of "duplicate" avoids having a large number of questions, "why the long metal tube on the ___" for any number of various aircraft. While not the same verbatim question text, it's the same quandary, all with the same answer.

@RalphJ Can you maybe add this question as a second duplicate? It also discusses the air data boom (for An-225 and the Buran).

It is a duplicate now with @sophit 's edit to that question, so I retracted my reopen vote.

@Someone: hopefully that answer answers your question in a satisfactory way


text:
Why are many parts of an airliner required to be triplicated, but not the "parts" most likely to malfunction (i.e., the pilots)?
Many components of airliners are installed with three redundant systems to reduce the risk of equipment failure causing accidents. However, there are only two of the "components" most likely to "malfunction" and cause an accident: the pilots. Why are there not three pilots to match the triplicated redundancy of other critical systems?

Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on [meta], or in [chat]. Comments continuing discussion may be removed.

Triple redundancy is often used when you need to know correct value even in case of single failure. Think (airspeed) sensor for example. (But the same can apply to output of flight computer or any other value in system.) The sensor has no (completely reliable) self-diagnostic, it is simply outputting one number. With only two sensors, one of which is malfunctioning, you get two different numbers and can't know which is the correct one. Average or any other "merge" will be for sure incorrect. With three sensors, you can sort the values by magnitude and take the middle one. It will be close to "correct" even if one sensor gone wild.
It is not intended for situations where 2 of three systems fail (because if failure rate is so high, that failing two systems simultaneously has still non-negligible chance, then failing all three won't be too far away). If you can isolate and identify failed system, double redundancy is sufficient. Or if it is enough to know "something is wrong", because there is particular action to be taken in response which is always safe.
Tricky part with failing systems is to know which has failed (and that it has failed). And here is triple redundancy and voting an useful approach.
Piloting of airplane is not decided by "voting", so adding a third pilot would not help in this sense. For human interaction and time-critical situations, having third independent opinion, even if maybe useful in theory, tends to not turn out so well in practice. I would expect (personal opinion only) that having three "redundant" pilots would make it less safe.

Counter point in which 3 pilot votes would have (probably) prevented a disaster is Air France Flight 447:
"He pushed his side-stick forward to lower the nose and recover from the stall; however, Bonin was still pulling his side-stick back. The inputs cancelled each other out and triggered an audible "dual input" warning."

@ROIMaison: There were 3 pilots in that incident

@BenVoigt but only two flying at a time

@ROIMaison 3 pilots at the controls would have caused a “triple input” alarm so I’m not sure how adding another pilot would help

If you read the article, there is one pilot who was pulling the nose up, and the other pilots (after each other) were putting the nose down. So if there would have been a 'vote', it would have been 2 votes for nose down, and one for nose up, and the plane could have recovered from the stall.

Engines are a good example of a case where single redundancy (two engines) is enough: you know if one stops working, and which one it was, and can land safely on one.

@Doryx: Yes you'd get a triple-input alarm, but if two sticks were commanding full nose-down while only one was commanding nose-up, you'd expect the avionics to obey the majority vote while also warning about it, unless there was a priority setting.  This would make the plane flyable (in a cumbersome way that required two pilots to coordinate their inputs) even if one of the three sticks failed in a way that commanded full deflection in some direction.  (Hopefully that failure mode is basically impossible, or there's a switch to give one stick the only vote.)

How's that going to be programmed? One stick says 3 degrees down, one 5 degrees and one says 2 degrees up. What to take now? Maybe the middle ground is the only one that will fail? How would you know for every possible action which of the three to choose. Or how do you coordinate 2 wide range inputs to be "close enough" together? What's close enough? Which one do you use then?

NIce point with AF447. :) But it rather shows that averaging is the worst failure mitigation scenario, more-or-less guaranty the result will be wrong. Idea with median is when one signal diverges, median will never pick it, so yes, median would work here too. OTOH one important assumption for redundancy is that failures are independent events. So it does not work when speed reading is lost bcs of icing (external event affecting all inputs simultaneously -- at least as long as you do not have sensors with different physical mechanism) and likely pilot errors are not independent events either.

The discussion in the comments about three flight sticks seems to presume that, in an emergency, they're only going to pick up or down - I'd expect someone to pick a third option, and make things further difficult in that case.

That all aside though, my understanding of the sensor issue isn't just normal fluctuation as well, but also for cases like single event bit flips caused by cosmic rays - they're more likely to happen when you're higher in the air, but they'll happen for one bit when they do - and humans are more complex than bit-wise information that won't be overridden like that.

@DonQuiKong: Good point.  It's not a simple up vs. down vs. neutral input, and requiring two of three inputs to match within some small range would make it hard to do anything.  Taking the median separately on all three axes (including rudder pedals) could lead to really wild behaviour if pilots didn't agree.  (Like AlexanderThe1st pointed out.)  The mean as a mixing function allows an outlier to have some effect, for good or ill.  Yeah, no obviously-good solution, so yet another reason this isn't done in practice.

@PeterCordes even worse - choose between 3 degrees up and throttle to 30% and flaps out as the first input and two other combinations of completely different inputs (probably doesn't make sense, but the point is, you can't look at every input in isolation).

I agree there are difficulties in combining/averaging/voting multiple inputs, but they are not the different in the 2 sticks vs 3 sticks case. From the text I quoted earlier, the 2 sticks were in opposite direction, so they cancelled out (which was also not the best course of action)

Having three or more pilots on board does indeed offer a wider margin of safety than two. This is called "augmented crew". Augmented crews are mandatory on long-range flights to meet crew rest requirements, and also happen as a side effect on check-rides. They are also universally used, even if not mandated, on acceptance flights, early in the life of the new model, and on many non-standard flights.
This study details the performance of augmented crews extensively.
Additional pilots in an augmented crew don't have controls and act in an advisory or supervisory capacity. More than two sets of controls aren't necessary, and they would enlarge the flight deck, increase its cost, complicate control mixing, and possibly have a negative psychological effect when a regular 2-pilot crew is used.
The tradeoffs against mandating a larger crew are:

Cost: Pilot hiring, training, currency, and of course pay
Dispatch reliability: It's easier to get 2 pilots available than 3
Extra weight: Permanent station and rest areas for larger augmented crews

Pilot error can be both of a positive nature (taking the wrong action) and a negative one (failing to take the right action). Augmented crews improve the latter and help catch the former. Three sets of controls might have prevented one or two conflicting input accidents that have happened, but could also slightly increase the rate of positive errors.
Overall, commercial aviation is a field of tradeoffs. More crew members can be useful, but they cost more as well. It's done when necessary. So far, the accepted compromise is to provide two sets of controls, but include jump seats to augment the crew occasionally.
P.S.
Personally, I feel that there is room for improvement in cockpit tech. AR helmets, as used in the military, can help in zero visibility and replace smoke hoods. ML can be used to augment autopilots with human input derived models, for higher autonomy. But overall the level of safety is good already, so it's not a priority in commercial design.

Do you have evidence that three sets of controls might prevent conflicting input accidents? It's not obvious. What is the "correct" input if one pilot banks right, one banks left, and one pushes the stick forward?

@DJClayworth It's "might" precisely because there's no evidence. In your case, there's no correct input. But in the case that one pilot has died / LOC / lost control, and voting logic was implemented over just mixing, two other pilots would take over more reliably than one.

The short answer is humans have more means to tell whether another person is making mistakes, compared to systems with limited, and predetermined, functions and test capabilities.
On the other hand it's not exact the common aerospace rule is triple redundancy. Actuators are as important as the pilots, they are needed to execute pilot orders, still most actuators are not triple-redundant.
The triple-redundancy is first used for sensors and computers, when you can't decide if a sensor/computer is delivering wrong data unless you can compare with (not one but) two other.
Before answering your question, let's keep in mind a reality: Risks cannot be completely mitigated.
Basic principle: Statistical significance
Any engineering activity is imperfect, and failures are expected to occur. The rate of failures can be further limited by adding protections. But protection design, implementation and maintenance have a cost.
A balance has to be found between cost, failure likeliness/consequences. This is globally known as risk management, and this is based on statistics.
The manufacturer, the operator, the crews and the passengers have no choice but to accept the unmitigated risks. Of course nothing prevent a manufacturer to design more safe aircraft, but usually this means a higher price and less sales.
However in order to protect crews, passengers and public, this industry is regulated to limit the residual risks to an acceptable likelihood. If we judge by the current frequency and consequences of incidents and accidents, this industry if by far safer than most other activities.
Current techniques used for risk mitigation include both the triple redundancy and the two-pilot crew.
Triple redundancy: Need arbitration
If you have only two systems and they disagree, can you tell which one is wrong?
You can't know. You need a third one to bring out a majority. From Wikipedia:

In this case you will assume the majority is right. This assumption is most of the time right, though this is not guaranteed, and accidents have happened due to simultaneous errors occurring in triple-redundant systems.
Pilots: Crew resource management
Most large aircraft can be handled by a single pilot, though in a degraded way. Having two pilots is already a mitigation for pilot incapacitation. The statistics for both pilots incapacitation is insignificant despite being common in movies.
For pilots, there is no need to have a third pilot to know if the other is starting to make mistakes, or is failing to react. One pilot, assuming he/she is not incapacitated, can evaluate the condition of the other and take control over if required.
In case of doubt a discussion can occur to clarify the situation and decide what to do. This possibility is at the base of crew resource management, and doesn't require a crew of three.
This is not a perfect process, but triple-redundancy isn't either. It's not clear whether involving a third pilot in the process would be real improvement, e.g. an unnoticed slow depressurization may affect the third pilot as well.
Actuators: Rarely tripled
Beyond decision making, there is the special case of actuators, to execute the decision. E.g. after a flight controller has determined what to do with the ailerons, the corresponding action must be triggered. Of course the corresponding actuators can fail.
Some of the important actuators are actually dual, e.g. both electric and hydraulic (hybrid actuators). But they are rarely tripled:

Source.
The preference in case of total failure of an actuator (or in the transmission chain) is to use other actuators on other surfaces to get a more or less equivalent result. This is the principle used by Airbus with the control law reconfiguration:

See this answer for Airbus laws.
E.g. if the ailerons actuators have failed, or the ELACs controllers, using SECs controllers and spoilers is a bypass.

Props to Therac for mentioning it, but a large number of these answers sidestep or ignore a very important point: everything must be a calculated tradeoff. Especially in commercial airline operations, every decision is made in terms of cost and benefit.
It may be nice to think that anyone may practice, "safety at any cost." However, this is not reasonable.
The safest option is not to fly.
To prevent airliner crashes, prevent airliner flights. This doesn't work out for a commercial airline. The whole point of the business is to fly people around. There are already trains and buses, which serve other purposes and have other advantages and disadvantages, for various reasons. An intentional choice is made, to be unsafe, and fly people around in pressurized metal tubes.
(I am not ignoring that commercial aviation is much safer than many other modes of transportation. Taking a human being off the ground, especially at Mach 0.8, is just inherently a risk, regardless how much you make it safer.)
Why stop at 3?
If you make the argument that 2 pilots is not enough, why do you think that 3 will solve all of the problems? Why not 4, or 7, or 118?
The existing number, 2, isn't arbitrary. Decades of experience has shown that for an average commuter hop, 2 pilots minimizes the dollars per safely arriving customer. Other longer flights are staffed differently.
Adding another pilot (or flight engineer, navigator, etc.) costs a lot of money. I suspect most passengers would answer no to:

If I charged you 650 instead of 300 for your 1-hour flight, and instead of a one-in-a-million chance of dying in a plane crash, you had a one-in-a-trillion chance, would you pay extra?

(The numbers are arbitrary but they're reasonable and demonstrative. Also most people are really bad at probability.)
Adding a third airspeed sensor also costs money. The amount of money it costs is way less though, and it provides a giant benefit when units 1 and 2 fail or give faulty readings. Redundant hydraulic systems are much more expensive, but commercial airliners tend to have them anyway because the benefit is sufficient to match the extra cost.
Note that this decision is also made very differently in military aviation because there are more and greater risks.
The more common solution to this problem is to make the airplane easier for a single person to fly (in the case of catastrophic failure of one of the pilots), and still be able to land in the case of a fairly significant problems. This solution is more common because there are many more means to solve it rather than requiring more pilots in the cockpit.

Military treade-offs are not so different, and survivability is the wrong discipline to look at for that. Look instead for reliability or System Safety.

Some systems are "redundant" only two deep, or not redundant at all.
One or two engines. Two wings. One rudder. One nose gear.
Why aren't there "3" pilots? Because many decades of commercial airline ops have shown it to not be necessary.

I don’t think a second engine or second pilot is redundant. A failed engine or pilot will be generally much more survivable than one of two wings being inop.

"A twin engine aircraft gets you to the scene of the accident more quickly" - pilot's aphorism

@FreeMan That was said about airplanes very different from modern airliners.

It is a common mathematical problem in aerospace industry (especially in space industry), how to protect your system against component failure.
And the solution to the problem is well known. And there are many solutions.
If you need to protect your system from a component failure triplicate the number of components is not enough (although there is an exception).
Say you want to protect your aircraft from a failure of a computer measuring the flight speed.
You need at least four computers to be able to establish the real flight speed in case of a failure of a single computer.
A more general answer is you need 3n+1 computers to mitigate the failure of n computers.
And you can't just pick the mean, median, or mode of the results of all four computers. There is an algorithm to establish the correct answer. As I said, there are many well known, ready made, easy to find algorithms.

2n+1, not 3n+1. Not only is 3n+1 excessive, it gives even numbers 50% of the time which is exceptionally bad for determining quorum.

@Shirik No. The correct answer is 3n+1.

There is an exception where 2n+1 is enough, but in general 3n+1 is needed.

Explain the math behind the 3n+1. Don't just write it.

Say we have nodes A, B, C. Say they measure speed. The node A has its own result, say 7km/s. A is asking B "give me your result". B says 7km/s. Then A is asking C "give me your result". C says 9km/s.  So what is the speed value? A has 7km/s and B confirms it. But A knows it cannot trust B. B may be reading 9km/s but is giving wrong result intentionally. So how can A know that B is saying the truth? You never know which node is faulty. What if the real speed is 9km/s but B or A is giving a wrong answer intentionally? You can apply the same logic when B is asking A and C.

This A,B,C reasoning also applies to A,B,C,D,...,Z.  Where does the 3n+1 come from?  Do these easy to find algorithms have published names?

Your "3n+1" example is wholly illogical. Aside from the fact that voting systems aren't implemented on the sensors themselves (node A MUST not care what B or C say; voting is independent of all nodes), even in your architecture, A would trust 7 over 9 because it came up with that answer itself. There's one sensor in disagreement and that should be thrown out. And that is also exactly why 3n+1 does NOT work. In such a model you would have A, B, C, and D, and you could end up in a situation where A and B report 7 and C and D report 9. Now you have no idea what to pick because they're equal.

@CamilleGoudeseune this algorithm is known generally as "quorum consensus" but in aviation specifically it's almost universally "triple redundancy" (which comes from the simple case of n=1, so 2n+1=3)

This answer (and, I fear, our comments so far) is a digression.  It does not even address the question, as @mins noted.

This answer might not be a digression, but in that case it is incomplete. If we model pilots as "subsystems that can fail, who might detect internal failures, and who might detect failures in adjacent subsystems by means other than disagreement", then we can apply math to come up with reasonable pilot numbers. But even then c*n+1 will never be 2.

This problem is known as "Byzantine Generals' Problem" and the solution is 3n+1. There is a special case where the solution is 2n+1, but it is a special case. Search for  "Byzantine Generals' Problem" and you will find better explanations than I could possible write. Search for "why 3n+1" as well.

authors: Vladimir F Героям слава


text:
Are glider pilots who are 14 or 15 years old more dangerous than those who are 16 when soloing?
With a student pilot certificate and an endorsement, it is legal to solo a glider at 14 years of age. When I was 14, I would have probably thought I was old enough to solo a glider, but looking back (I'm 17 now), I don't think I was mentally mature enough then. Soloing at 14 years old just doesn't seem safe to me (although maybe when I'm 20, I'll think soloing at 17 sounds like a bad idea, even though it sounds fine to me now!).
Are there any statistics available showing whether 14- and 15-year-old glider pilots are more likely to be involved in accidents than 16-year-olds with comparable experience when soloing?

Why do you think you weren't mature enough?  Who was at risk? (both are genuine questions... nothing implied)

All the students who go solo have been signed off by a CFI, so there's that check on things. If the CFI (and, in most cases, the owner of the glider) have enough reservations about the student's maturity, they have the ability to keep it from happening (at least with their equipment or certificate on the line).

+1 for recognizing that future self will realize that past self was far less competent than current self thinks he is.

There almost certainly aren't enough statistics to say anything one way or another. As of December 31, 2021, there were only an estimated 552 people with student certificates in the below-16 age group according to the FAA, compared to 250,197 total student pilots and 25,826 certificated glider pilots. And keep in mind that just having a student pilot certificate is by no means a guarantee that you have soloed!
That said, I think it's obvious that there is nothing magical about the age 16. A pilot that turned 16 today is not significantly safer than they were yesterday. But you have to draw an arbitrary line somewhere.

There are plenty of stats about driving cars at young ages. Not 100% comparable, but plenty of correlation, I would expect.

I used to teach a summer camp for teens at an old glider club. It was an intensive 2 week course where the kids were brought to license at the end of week 2 (most of them). The kids were Canadian Air Cadet members who didn't make the cut for glider pilot scholarships in the military program. Their parents paid a flat fee and the kids came and lived on site for the two weeks. As an instructor, I would do about 75-85 instructing flights during week one.
We would get around 14-16 kids, aged 16-18. There was a consistent cross section; although in general, the older the better, a few of the youngest ones were always more mature than a few of the oldest ones.  A few we called "top guns" who were super fast learners. A few always had to come back to finish up a couple weeks later, and one or two would wash out as we realized they just weren't cut out for it. Outside the cadet program we did have occasional 14 or 15 year old students.
If if you took 100 14 year olds and 100 17 year olds, you'd have more 17 year olds than 14 year olds you'd be willing to trust an expensive machine with. But there will so some 14 year olds who you will assess as mature enough to be trusted with careful supervision.
Below 14, the likelihood drops off sharply. So the cut off was set at 14, because there are likely to be some kids who are mature enough, as assessed by the instructors. Below that, most kids are just finishing up emerging from childhood where their world is half fantasy, so going down to 13 or younger is pushing it a bit too much.
On the other hand, there will be some 17 year olds who shouldn't be allowed anywhere near an airplane. And the occasional 35 year old come to think of it.


text:
Are aviation training standards being lowered for diversity, equity, and inclusion?
Have there been documented cases of training standards being lowered, or other risk-increasing actions being taken, for the purpose of increasing diversity, equity, and inclusion (DEI) in the aviation industry?
The mere existence of DEI policies does not necessarily imply that standards are being lowered. If an airline decides to prefer hiring pilots from minority groups when given the choice between two equally-qualified candidates, that's a DEI policy, but it does not involve lowering standards. If, however, an airline would prefer a less-qualified pilot solely due to minority status, and there is evidence of such a policy, that would be a good answer.
I am not asking for opinions. I am asking if there is documented evidence of at least one case of standards being lowered to promote diversity. Please do not debate the legality or ethics of DEI in the comments.

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The only case I'm aware of isn't so much a drop in standards, but a bizarre sort of dirty trick incorporated into an Air Traffic Control preliminary screening questionnaire during the Obama admin. If you answered that your worst high school subject was "science" to one of the questions, you were moved to the top of the list. The "correct" answer was broadcast to minorities only, somehow, to get the word out.
You may think it sounds too crazy to be true and I'm talking through my hat, but it did happen and there is in fact a class action lawsuit filed against the FAA, (Brigida vs FAA) filed after the scheme leaked out, by people who had spent thousands at private ATC training colleges and found out the deck was stacked against them if they weren't a beneficiary of the information.
The questionnaire was later dropped, but it seems to have gone on long enough to get a lot of "non-beneficiaries" pretty upset.
Reducing standards in training is another matter, and I have seen no evidence of that. But if it was happening, it would show up as, say, an internal policy where a minority trainee would be allowed additional simulator sessions if they were struggling, or possibly they would be allowed a "1" score (items are graded 1 to 4, with one being a fail) on a check ride item where that would normally fail a pilot. On the other hand, there is some discretion afforded the people doing the training, so that sort of thing could be happening unofficially.
If it was an actual policy though, I think you'd get a pretty big outcry from everybody, including black, brown and female pilots who did meet standard.
I think if you polled the pilot community you'd be hard pressed to find anyone who wasn't fine flying with anybody who met standard under the standard training conditions like everybody else, even if they were purple with spots.
Probably if you peruse PPrune Forums no doubt you'll find a forum channel with this debate raging on. There was once a Boeing Simulator instructor who worked in S Korea for many years who unloaded on PPrune about training of Asian crews (related to cultural issues, not intelligence or skill). So if anything is happening with DEI in aviation, that's where you'll find out about it.


text:
Are flights in fast jet streams more dangerous?
This article from Not the Bee (note that this is a right-wing site, and the article includes a paragraph making fun of diversity, equity, and inclusion initiatives, so don't click the link if that would bother you) reports that a 265 mile per hour jet stream made several airline flights faster than usual. The author seems to believe this made the flights more dangerous:

Is an hour off your travel time worth it? I kinda feel like it would be. Sure, your chances of dying are slightly higher, but I'm an American and an hour is an eternity.

I don't see why this would be the case. Would the fast jet streams have negative safety implications?
This isn't a particularly reliable source, especially on aviation-related topics, and they also have political motivations for exaggerating the danger of aviation.

At the risk of wandering down a deep, off-topic rabbit hole, why do you think a conservative site would have "political reasons for exaggerating the dangers of aviation"? Generally, it's the more liberal folk who are against aviation for the political "save the environment" causes...

@FreeMan it's not conservatives in general; this site in particular likes to point out issues with aviation safety and claim that (a) there has been a recent significant increase in safety incidents and (b) this increase is caused by training standards being lowered for diversity, equity, and inclusion initiatives. Basically, the more dangerous they can make aviation in recent years look, the more "evidence" they have that DEI is harmful.

@FreeMan to summarise very broadly, they think that aviation is "getting more woke" (based on a couple of stories about hiring practices at the FAA, replace "woke" with DEI, affirmative action, political correctness, whatever boogeyman du jour makes sense for you), that "wokeness" is bad, and therefore it must be causing bad things to happen. They will then find evidence to conform to that hypothesis, for a certain standard of "evidence".

Ah, gotcha. Have never been to "Not the Bee", so I wasn't aware of that. I don't, in general, disagree with their stand on that. I want my pilots well qualified. I don't care what color their skin is or the arrangement there reproductive bits may be. I just want to get to my destination and not die along the way...

The paradox of inclusive politics is,  that they aim to fade "individual qualities", but they actually do the exact opposite. Suddenly ethnicity, sex and other totally indifferent denominators are a major consideration overriding substance.

@FreeMan well yes, but you've already fallen into the trap of accepting their framing. Vanishingly few people believe otherwise, the general belief is that perfectly qualified people are excluded from being pilots due to these irrelevant parameters. What they're reacting to is things like legally blind people being hired at the FAA, which is not a real problem when their jobs are writing reports and emails.

I find it hard to believe that someone would object to a blind person being hired to write reports and emails. I fully realize and accept that there are some truly prejudiced idiots out there, but no amount of "DEI" will ever change their minds. They're also a very small minority. Not the vast majority of "your white so you're privileged, ergo sexist, racist, whateverist" that is being painted. </off-topic>

@llama And I always thought that people were excluded for being poor... not because of race/gender/sex/etc...

All other things being equal, is it not a truism that flights at higher speeds might, and at extreme speeds will be more dangerous?

@RobbieGoodwin considering that crashing from cruise altitude is unlikely, it's not obvious that that applies in this case.

@Someone  Sorry. I now absolutely support your doubt and I suspect Not the Bee fell into the same trap I did: failing to notice the flight was going with the wind.
What I suggested very much applies in this case, but the opposite way round. It remains true for a given air-speed but in the same direction a faster Jet Stream could give greater ground-speed with less air-speed…
Average Jet Stream speed is ≈110mph, so in the direction of flight, 265-110 gives what? Much more than 100mph extra ground-speed for less air speed. That should mean more, not less safety.

Horrible example of journalism aside, any risk would come from clear air turbulence at the edges of the jet stream and the slower moving air.
In other words, it isn't the top speed of the air relative to the earth that affects safety, but the gradient on the way to getting up to the fast moving air mass.

The "journalist" may be naively comparing it to driving faster on a road.

In both cases the danger is not the speed/velocity itself but the sudden declaration when you hit something stationary. Doesn’t matter if it’s a wall in the case of a car or slow air in case of an airplane.

This of course is true, but begs the question of what happens to the gradient as the jet stream speed changes - do we have constant gradient and a changing boundary thickness, constant boundary thickness and a changing gradient, or (as I suspect) a more complicated situation with further variables

Worth noting: 'Journalism' is no more the goal of "Not the Bee" than it is of Last Week Tonight or The Daily Show. It's designed to be (very biased) humor, not journalism. Though this article comes across as uninformed even by that standard.

"Journalism" is no more the goal than it is of ABC/NBC/BBC/Fox or other "news" agencies, either. They're all pushing their agenda. Whether you think they're a good guy or bad guy depends only on whether you agree with the agenda being pushed. Also, they're all pretty uninformed when it comes to technical topics of any sort.

@FreeMan On editorial bias, absolutely. On basic facts, the ones where their news channels call themselves "journalists" (ABC/NBC/BBC) are always going to report those more accurately than organisations which only claim to provide entertainment (Fox).

@Graham, does Fox News actually "only claim to provide entertainment"?

The difference between a car and a plane is that in an airplane speed is what keeps you in the air. Of course that's air speed, not ground speed, but if the jet stream goes all the way to the ground then that's a more interesting problem. And ground speed isn't useless, either, if you're going faster then you have a larger (literally) choice of emergency landing sites if you become a glider.

@Graham On basic facts, they're all equally bad in not reporting the basic facts, as none of them do. Not ABC, not NBC, not BBC. Almost none of the news agencies actually provide you "basic facts" and will always include opinion and bias. To think otherwise is more naive than using The Onion as a factual news source. If you want "basic facts" you need to go to news reporting agencies that feed the information to various news channels. Those news channels, like Fox, NBC, BBC, CNN, ABC, take those basic facts and then dress them up in fluff for you.

@Graham someone forgot to check snopes (litterally 5 seconds of googling) before posting something online.., Now we know someone else who doesn't check their facts.

Yes there are hazards, and you do want a captain who understands them and takes precautions. However anybody with an Airline Transport Licence would be expected to know about them, and the airline itself will have specific internal policies for operation into and out of jet streams.
The main hazard of jets is they are a major source of Clear Air Turbulence. Jets associated with fronts form in the warm air corner, on the warm side of the frontal boundary and under the tropopause. CAT occurs in the shear zone along the edge of the jet, typically on top of the jet at the tropopause or along the frontal boundary adjacent to the jet. There are other types of CAT, which occurs with sudden changes in wind velocity not associated with convective cloud, such as under the crests of mountain waves where rotors can form.
Jet streams may be indicated as a probability in weather charts, by pilot reports, or you may just find yourself entering a jet by the sudden ground speed change or heading change (if you're flying across it).
Lenticular clouds are another warning sign of CAT, the clouds indicating the mountain wave top, which means you can expect CAT blow the lenticular cloud.
In any case, if CAT is expected, you normally will slow down to Turbulent Air Penetration speed, and make sure everyone is strapped in.  If CAT is really severe, and you are going too fast, people who aren't strapped down can get hurt, and there is an outside chance of damaging the airplane.
So basically the jet stream itself is not a problem, but the turbulence associated with shear zones at the boundaries is. And if you blundered into a jet that was a headwind you hadn't planned on, you might need to shift your route to get out of it.
To be clear about the concerns of DEI in the industry, it's not about resistance to minorities and women in the flight deck. It's a concern about standards being reduced to meet arbitrary DEI targets, because such targets, if enforced unreasonably by management under the gun to do-or-die due to political pressure, introduce a basic math problem; that is, the quota target necessarily reduces the talent pool, and if a directive from on-high says meet the target or else, reductions in standards may be the only option to meet the quota. That's the key concern.
If the US, the Colgan Rule, that requires 1500 hours to fly transport aircraft in airline operations, had a similar perverse math effect, by reducing the talent pool by excluding top notch copilot candidates just because they had less than 1500 hours (many of whom were likely female and minority). Regional operators were bitterly opposed to this because it put them in the position where they were forced to discard a superstar candidate's resume with, say, 1300 hrs, in favour of midwit candidate's with 1700. Such an arbitrary limit had little safety value in reality.

The funny thing there is that both pilots in the Colgan crash had more then 1500 hours...

Yep. None of it ever made any sense. In Canada there is no such thing and the Regionals still take kids with 4-500 hrs, sometimes right from the schools, but for the really green ones they give them a more comprehensive training program than the normal 3-week fire hose initial type course.

Yeah, $200K worth flights (after flight school) before you can become a pilot? becoming a pilot is not for the poor.

Nobody ever went from a flying school to a regional airline in the past. When I was young you needed a couple thousand hours before they would look at you.  You get your ratings, and go fly for 3rd tier carriers, or instruct or go fly the bush, or whatever. The path is there for anybody who can finance a commercial lisc. Much easier now, since the shortage is so bad and everybody is crying for pilots.

One common way to measure accident rates is in Hours Flown per Incident.
Typical accident rates in General Aviation are about 4.5 incidents per 100,000 flight hours. I cannot find a reliable source for the rate for Commercial Aviation flights.
Note that an "incident" is not one of the big fatal crashes that makes news, but any incident that results in damage to a plane or passenger.
When the jet stream makes a plane fly faster, it gets to its destination faster. Fewer flight hours means less time for an incident to occur, which implies greater safety.
However, most aviation accidents happen during critical phases of flight such as departure and landing. Once a flight is established in cruise in the jet stream, there's a lot less that can go wrong. There's minimal maneuvering, and minimal changes to power or configuration.  Saving time in the jet stream is really reducing time in the safest part of flight already.
Overall, a fast jetstream should have very minimal impact either way on safety. I estimate it might make flying a little bit safer due to the flight time saved.

"I estimate it might make flying a little bit safer due to the flight time saved." But if most accidents occur during landing and takeoff, and the jetstream speeds up the flight, then you will have more accidents per flying hour on average.

@Nobody  Exactly.  So it makes the naïve statistics look more dangerous, even though the actual risk is almost certainly lower.  A perfect example of "Lies, Damned Lies, and Statistics."

@abelenky... And I thought it was the 37% of all large air plane accidents between 2008 and 2018  caused by areas of high turbulence--Such as cough the airspace right around the jetstream-- that made using the Jetstream dangerous.

If you can manage to consistently fly with a strong tail wind, then you can fit more flights in your schedule.  This increases the number of takeoffs, landings, and ground movements.  Most of the (small) danger is near the ground.
As the other answers say, the jet stream has no meaningful risk for a fixed number of flights.  If you have a fixed amount of time and want to squeeze in more flights, you can expect a minuscule increase in risk.

Small consequence would be arriving with more fuel on board than expected, leading to a slightly higher landing weight.   This would increase the consequences of any poor landing, by having more combustibles on-board.
This is superior to the inverse, where the plane has a headwind, a slower speed, and arrives at the destination with negative fuel.

The accuracy of modern weather forecasts & reports really negate this. If I'm planned to land with X fuel on board, that has been done accounting for the winds. An unexpected wind can lead to landing with unexpectedly high or low fuel loads, but that's separate from the strong (but known) jetstreams of the OP. If anything, strong tailwinds make for slightly lighter *takeoff  weights, since less fuel is required for the flight. That slightly reduces the risks, should anything go wrong during or shortly after takeoff.

TL/DR
It is more dangerous because of the area of high turbulence around the jet stream, but as long as the passengers/crew are properly strapped in when entering/exiting the jet stream the risks are not higher than flying in general.
Details
According to a NTSB report in 2021, 37% of aircraft accidents on large commercial planes involve areas of high turbulence...
To be fair the jet stream itself is not very turbulent, it is the CAT (clear air turbulence) around the jet stream that can be problematic. I can think of one instance off the top of my head a 747 flew into the CAT around a jet stream and had one fatality and multiple injuries because they were not strapped in.
So, the answer to the question is... Jet Streams are not more dangerous. But entering/exiting the jet stream exposes the airplane to pretty high turbulence caused by shear bands.
This poses little risk to the airframe which can easily withstand the forces... but does pose a risk to passengers/crew members if people are not properly strapped in. All of the injuries involving the jet stream that I know of involve passengers/crew who were not strapped in.

As others pointed out, there are two potential factors that may increase the risk.

increase in landing weight, due to less fuel burned during the flight;
densier landing schedule at the arrival airport, so more traffic, so increased risk at the critical landing moment.

However, the site in question forgot to mention that reduced flight time at high altitude reduces the exposure to radiation for each passenger.


text:
What authority does the owner of an aircraft have as a passenger?
If Alice, who owns an aircraft and may or may not be a certificated pilot, flies in her plane as a passenger with her friend Bob as PIC, what authority, if any, does Alice have over the flight that an ordinary passenger would not?

It is an interesting question. On maritime laws (origin of most aviation laws) the owner has more power compared to the master (captain), and a captain should (if possible) ask the owner what to do in case of need/accidents. Obviously in aviation the timing are much different. So I expect the rules changed (why? and how?)

They have full authority over their own personal relationship with the pilot.  For example, if the pilot does something they don't like they can choose to never let the pilot fly their airplane again.  Or, if they have hired the pilot, they can fire the pilot.
However, in the eyes of the FAA they have no authority over the conduct of the flight whatsoever.  If the owner persuaded the PIC to do something against regulations in a non-emergency under threat of firing, it isn't the owner who will earn a flight violation in their record... it is the PIC.

Thank you! What if the owner tells the pilot to divert to a particular airport, and this is neither necessary for nor harmful to the safety of the flight?

@Someone The same as if you're driving someone's car and they tell you to divert to a different destination than originally planned. It's between you and them.

This isn't a matter for the regulations. The PIC and owner of the plane should have a private agreement on how the airplane will be used. This can vary from no authority if the PIC has leased the aircraft from the owner with no restrictions on its use to a great deal if the PIC is hired by the owner to transport them somewhere.


text:
Can cold thrusters/roll posts be used to control/stabilize an aircraft (like a satellite)?
Aircraft use control surfaces to control their motion/direction. Would it be a good idea (i.e., more efficient, less weight, better responsiveness, less drag, etc.) to use thrusters/roll posts to control roll, yaw and pitch, like the roll posts an F-35 uses for hover?
this question refers specifically to a continuous flow system like the F-35 roll posts. no rockets no turbojets

Do you include missiles under the aircraft label? Because that is about the only case where thrusters can and have been used to provide increased performance, but I realize not everybody would call something like the 9M330 or 9M338 missiles "aircraft".

The space shuttle used its RCS (Reaction Control System) for the first phase of entry.  Gradually, these thrusters were disabled as it reached enough dynamic pressure to use aerosurfaces.  By 45,000 ft and Mach 3 the RCS was fully disabled:  https://spaceflight.nasa.gov/shuttle/reference/shutref/events/entry/

There are several ways to do it, rockets or turbojets. Rockets have a problem with fueling them, turbojets are very difficult to find a place for that offers reasonable leverage.
Roll posts on the F-35B are not really thrusters, but rather use redirected engine thrust. They're not light either. Engine thrust at high altitude and airspeed is considerably lower than at sea level, while required control forces are larger.
Short version: The reason why control surfaces are better for control than cold thrusters is Lift coefficient, or more precisely the lift-to-drag or lift-to-thrust ratio.
An engine directed in the direction you want to apply force in has a lift-to-thrust ratio of 1. Each newton of engine thrust, gets you 1 newton of force. To produce 1 kN of force from the roll post, you lose 1 kN of thrust.
An airfoil at some angle of attack has a lift-to-drag ratio generally between 5 and 25. By deflecting an airfoil to get 1 kN of force, you only lose 40-200 N of thrust to drag. Thus, it's a much more efficient way to change your direction.

All in all, using thrusters of either type would result in...
Less efficiency: Thrusters require fuel, control surfaces don't. And if they're rocket type, they even need to carry the oxidizer.
Cold thrusters don't require extra fuel directly, but they "steal" main engine thrust, so you get slightly less efficiency.
More weight: An engine can produce 10 times its weight in thrust for 1 unit weight, but an airfoil at high angles of attack can produce a force 100 times its weight. The big weight problem will the be the added fuel, especially for rocket engines that need a lot of oxidizer. Plus, you still need the control surfaces, because they're the only way to adjust your aerodynamics for sustained flight. Thrusters could only be used to accelerate the initial maneuver.
Better responsiveness: with rockets, but a lot of fuel is required for those.
Worse responsiveness: if you reduce control surface size and use turbojets (they take a long time to spin up). The same if control surface size is unchanged.
Same responsiveness: with roll posts/cold thrusters.
Less friction drag: if control surface size is reduced. But since you still have to keep your control surfaces, just can get them smaller (the largest deflections are used at low airspeeds), not much less. Also, the added induced drag from the extra fuel may make up for it.

Overall: There's a reason that even rockets typically use fins (control surfaces) when possible. The only things an aircraft may need thrusters for is things that can't be done with control surfaces.
For instance, roll posts are used on the F-35B because control surfaces don't work at zero airspeed. Thrust vectoring has enabled some maneuvers beyond the normal angle of attack envelope.
If not for the oxidizer problem, there could be some applications for thrusters for unusual maneuvers, strictly in addition to control surfaces. As it stands, their thrust is too expensive to get, compared to force from the control surfaces and even to main engine thrust.

the question was specifically about a roll post like system in flight. not rockets and turbojets. but thx anyways

You should clarify that in the question, because roll posts are different from thrusters. Anyway, I've addressed that too.

reread your modified answer. thx. great explanation


text:
How to estimate blade interference in a propeller or fan?
The ideal propeller has one blade. For obvious reasons, that would be impractical.
However, adding more blades causes each blade to operate in each others slipstream/downwash.
How to quantitatively estimate this interference?In other words, what is the real angle of attack and airflow speed seen by each blade

Question seems incomplete @toshi-ba

Single-bladed props with counterweights actually do exist.

There's a pun to be made here about the question completeness and single-blade props, I'm sure.

just completed the question. sorry i signed up while typing the question

The problem with this question is that you are asking for an estimate of something without defining the nature of the metric in which you want your answer. The last sentence is also a different question.

well, more specifically how to estimate the angle real angle of attack seen by the blade. as well as the real airflow speed

For a simple 2D approximation, you can do it in a similar way to how you would analyze the effect of wake on a tailplane or any other body, i.e. by solving the flow field around both at the same time.
Since the movement of the  blades is cyclical and the flow is subsonic, each blade affects both the ones ahead and the ones behind it. Therefore, you would would need to solve for an infinite number of blades simultaneously so that the one in the middle would have a realistic airflow, but since the effect of the N-th blade will tend to nill, a good approximation can be had with just a few blades on either side of the studied one.
The process would look like this:

Choose the spanwise station of the blade you are interested in and the operating point (rpm and forward velocity) you want to study. These will give you the effective angle of attack for the blade station.
Knowing the angular blade spacing around the hub, the spanwise station you selected, the rpm and the forward velocity, find out where the first airfoil will be relative to the second one in a 2D representation.
Solve the flow field for an effectively infinite number of airfoils spaced this way. In practice solving for a relatively small number of blade instances will provide a good approximation of the real flow on the central blades in the series, as the ones on the edges are only used to provide boundary conditions resembling the real world case:

thx for the answer. instead of studying the whole flow field, can i analyse the blades as series of diffusers/channels, (which would be the spaces between them)

A "series of diffusers/channels" is essentially the same, it all depends on how you postulate your boundary conditions and how closely they need to match the real world, i.e. how far away from the blade do you want to take effects into account.

It's possible to calculate the losses for a given configuration, but it's not an easy task. Meanwhile, there is a hundred years worth of testing and experience with propellers, so if you have a classic prop design and want to know typical trends, you can find most of the results in the literature.
One of the best classic sources on this topic is NACA-TR-640 (1938!)
I'll quote one graph from it that is directly relevant to the question:

As can be seen, adding an otherwise identical blade causes a power loss of maximum 6-8% per blade (in static conditions, at zero speed), and very little (1-4%) in normal flight conditions.
Comparison of the respective propulsive efficiency curves (Fig.35 in the work) is even more interesting: the difference is even smaller, and in some regions (when the blades stall) the multi-blade props can be more efficient than two-blade ones.
In practice, when you need to absorb extra power from the engine and are constrained by the diameter, you have to increase solidity of the prop. You can do it either by adding blades or by increasing the blade chord. The paper demonstrates that adding blades is better in terms of efficiency. Thus the premise "The ideal propeller has one blade" is not necessarily true, given the realistic constraints.

Power loss due to swirl is up to 10% of the applied power, depending on the applied thrust. From Prouty, Helicopter Performance, Stability and Control.


text:
What are the commercial benefits of VTOL?
there are a lot of companies doing R&D on VTOL aircraft. I understand their necessity for the military, but for civilian aviation, there are a very few application that requires it( medevac, search and rescue, offshore platform).
do you think vtol has a future for passengers transportation, or is it another silicon valley/uber/ youtube gimmick?
my question relates more as to the very nature of vtol, rather than the type of tech used(helicopter, multicopter, magical anti gravity device )

There must be a way you could ask this question that has one "best" answer and isn't mainly asking for an opinion from answerers.  It has the potential to be a good question if you can find that way.

The question is not bad, but a better way to phrase it is "What is the commercial benefit of VTOL aircraft?" rather than "Is it here to stay?"

This is potentially opinion-based, but I can tell you what I have seen working in the aerospace industry alongside (but not inside) some of these companies testing VTOL aircraft for commercial usage.
One major benefit of a VTOL aircraft is that it can take off and land vertically, like a helicopter, in nearly any type of terrain. This eliminates the need for a runway and instead you need a helipad, or in an ideal world, a few parking spaces.
So why not use helicopters? Well, helicopters are very inefficient compared to fixed-wing aircraft when flying any considerable distance.
Take for example a proposed flight route of Boston to New York City. A VTOL aircraft could pick you up from a parking garage or parking lot in Boston, reorient itself in a "horizontal" mode, fly the ~200 miles or so to New York City, and land on top of a building. No need for airports, no need for inconvenience.
Different companies give different quotes, but you'll see people quoting up to 90% greater efficiency on these sort of routes, making it affordable to perhaps not your average middle-class, but perhaps your slightly above average middle-class.
Given the increase in efficiency, it's certainly likely that this technology will be used commercially until something better comes along.

thx for the reply! what would be then, commercially, the ideal size of a vtol aicraft, operating point to point?30pax? 50 pax?

@toshiba VTOL as given in this answer is more about 1-2 pax (so ideally no pilot) - the physics in the vertical phase dictate ideally a helicopter, every decrease in size of the lifting disc means higher airspeeds (=higher danger of flying debris, higher noise), So envision the noise and debris-danger of a very small 2-seater helicopter and where you would allow something like that to start and land on a daily basis and you have the approximate applications....